The Synchronous Optical Network (SONET) standard is used for communication on fiber optic cables between routers in a telecommunications network. The fiber network uses multiple cable paths operating in tandem, such that data that fails to arrive at a destination (due to a fault in one path) will arrive over the tandem fiber path. However, Internet Protocol (IP) routers that have optical ports based on Packet-over-SONET protocols have not been protected from optical receiver device failures or from optical fiber breaks with any kind of hot standby immediate patch protection mechanism. Typical designs depend upon external routing of IP packets and flows to restore packet traffic around an optical failure in either the outgoing or the incoming ports of the router. This method of protection is very slow and is very cumbersome to engineer and to administer. Without fast acting hot standby protection, a network must be engineered with duplex and multiple routers and with less than fully utilized traffic capacity on each port. Then in the event of a facility or port failure during operation, all traffic must be redirected from the failed port to another port, which is available but underutilized and which has enough intrinsic capacity to carry the additional traffic under such a failure circumstance.
The first problem is not what happens once the failure occurs, but the way the network must be engineered to provide this complex protection structure. Once duplex routers or multiple routers are engineered into the network to address this type of failure, then typically it is required to engineer additional link capacity into the network between those routers. Whereas an unprotected network might require only a single trunk that is 100% utilized between two routers, a protected network under current technology requires a second trunk. The utilization of each one of the trunks in the absence of failure falls to only 50%. This increases the cost not only of the equipment, but of the router itself that now includes redundancy, software costs relating to the intervening network capacity, fiber optic transmission capacity including increased overhead traffic between routers, and administrative and engineering effort.
In prior art schemes an internal failure within one part of a router would have to be protected by rerouting of the trunk outside of that router, perhaps encompassing several other routers in an existing network. Failure of a cable at a router can in fact propagate significantly far through a network, resulting in substantial confusion to the network as it adjusts to reconfigured routing. The network must broadcast to much of the Internet any IP addresses, for example, that have changed. Thus, small localized failures produce impacts that ripple out through the network, even though their original cause may not have been significant.
Not only do the packets get re-routed, but there is of necessity broadcast information that has to be sent to various routers to handle the re-routed traffic. In situations where outages occur from time to time, this can become overwhelming to a network. Even in the best case, the time to perform a repair and restore the original configuration can cause network traffic to slow dramatically. Again, this affects the capacity of a network, which in the initial stage would have to be engineered for higher capacity than would otherwise be necessary.
A common problem is an intermittent fault in a network, coming into and going out of service repetitively, thereby causing the generation of rerouting messages almost continuously through the network, known in the industry as “route-flap”, resulting in much non-useful traffic.
Consequently, there is a need in the optical network art for router systems and methods that provide protection in the event of a failure, with a smaller investment in equipment and engineering effort than in the prior art. Further, there is a need for router failure protection that requires minimal disruption and reconfiguration of the larger network, and that provides seamless continuity of service in the event of a single point of failure.